Position switches are used in the industrial and in the private sector and serve to safeguard a danger area, such as is defined by a machine or production system, for example, with which danger is associated. Examples of the use of position switches of this kind are in safety engineering, systems engineering, automation engineering and also in building services engineering. In this environment, doors, flaps or other moving objects, for example, which are used to gain access or entrance to parts of the machine or production system, must be safeguarded.
For example, the particular object may be detected in the safeguarded position and, if necessary, can be latched in the safeguarded position by way of a holding-shut device. For this purpose, an actuator is usually attached to the movable object, which is localized in the position switch in the safeguarded position. The position switch in turn detects the presence of the actuator and, if necessary, can trigger a holding-shut device when the actuator is detected.
A holding-shut device, that is to say a latching of the actuator in the position switch, is expedient when after removal of the object from the safeguarded state, such as for example the opening of a door to be safeguarded, the machine causing the danger cannot be switched off directly in a timely manner before a user is able to move into the danger area.
In the past, a range of different position switches has been developed for these or similar applications. Here, the holding-shut mechanism is generally realized by way of a drive based on spring force or a drive based on magnetic force, in both cases the drive being intended for blocking the first rotatable locking element and thus for latching the actuator.
Furthermore, position switches are known, which have switch units, which are at least partially actuated by the actuator, thus indicating the operational state when triggered, in which the actuator must be mounted but not necessarily latched in the first rotatable locking element. Further, the position switch can have a switch unit, which can be at least partially actuated by a solenoid power drive. If the solenoid power drive is used both for the holding-shut device and also for triggering at least one switch element of the switch unit, then this can be used to indicate whether the system is being held shut or not.
The actuation of the switch elements by the solenoid power drive has often proved to be difficult, as large switch travel distances are usually required. In addition, it is desirable to use six or multi-pole switches while deploying standard switch elements, wherein an appropriate switching force must be applied, which must be guaranteed by the control and supply of the solenoid power drives via an ASI bus or additional power supply. With standard switch elements, a separate actuation of switch elements arranged in series is the only suitable method of avoiding this disadvantage, in a similar way to cruciform lever switches. In most cases, coils with higher powers are absolutely essential, as the necessary magnetic forces can only be realized using a correspondingly high current consumption.
For safety reasons, the holding-shut action must be guaranteed when locking the actuator using the solenoid power drive. For this purpose, it is often required to lock the actuator in the inserted state only when the coil is energized. If the coil is not energized, then the position switch releases the latch. This is expedient, for example, in the case of a power failure, in which the safety area must remain accessible even when the power supply is not available. The reverse case can also be relevant in which the interlocking holding-shut device latches the actuator in the inserted state when the coil is not energized. Depending on the application, this effects the exact opposite, namely the safety area is also inaccessible during a power failure. This last variant is expedient, for example, when there is a danger, which originates from electrical equipment running on, or from hazards, which do not originate from electrically driven machines, equipment or systems. The holding-shut device of the position switch must also guarantee that locking when the actuator is not inserted and unlocking of the actuator in the inserted state are reliably prevented.
EP 1 533 826 A1 discloses a position switch, which has a holding-shut mechanism. The holding-shut device works with a locking wheel and a locking element, which are mechanically connected to a large number of components.